In a typical helicopter layout, a fuel tank is located in a lower portion of the helicopter and the main powerplant driving the helicopter rotor is located in an upper portion of the helicopter. Fuel is drawn through a fuel pipe from the fuel tank by means of a suction pump located adjacent the main powerplant. This suction configuration is preferred as it mitigates fire hazard in the event of damage to the fuel pipe between the tank and the pump, because the pressure differential means that air is drawn into the fuel pipe rather than fuel spraying out of the pipe which would be the case if the pump were located in the fuel tank and which would constitute a potential hazard. However, as helicopters get larger the fuel head between the fuel pump and the tank increases, meaning that the suction required increases. Also, particularly in military helicopters, as the manoeuvres that the helicopter can undertake become more extreme, there is a risk that a combination of the head of fuel between the pump and the tank, and the high acceleration experienced during extreme manoeuvres mean that the absolute pressure at the inlet to the suction pump may approach or fall below the true vapour pressure of the fuel. This can cause fuel vapour to be evolved, and dissolved air to come out of solution, and if the proportion of gas and/or vapour to liquid fuel at the inlet of the pump exceeds the pump capability, the fuel flow to the powerplant is likely to be interrupted or significantly restricted, thereby resulting in loss of engine power or an engine failure.